The present invention relates to blood flow measurements and particularly to the elimination of perturbations in the blood flow waveform caused by mechanical movements of the body.
It is known that the strong ejection of blood from the ventricle of the heart into the arch of the aorta creates a transfer of mass because of the blood movement. This mechanically shifts the center of gravity of the body, which in turn creates reaction forces which act upon the body. As a result, a small bodily displacement or recoil is created which is synchronous with the ejection of the blood. These bodily displacements are recorded by ballistocardiographs, which display ballistocardiograms showing the movement of the totality of the body.
One type of ballistocardiographic apparatus is disclosed in U.S. Pat. No. 2,684,671 issued on July 27, 1954 to S. Mendelsohn wherein a displacement ballistocardiogram is recorded by photoelectric or electromagnetic detection apparatus near the leg shins of the patient. The recordings are used to diagnose various conditions associated with malfunctioning of the heart and aorta.
It has been found that a heart synchronized ballistic artifact is present when making blood flow measurements on the limbs of a living being when a magnetic field is applied in the area of the limb for producing an electro-magnetic blood flow signal. The limb being a conductor, the movement causes induction of voltages within the limb. The amplitude of this ballistic perturbation is so significant in limb measurements that it distorts the true blood flow waveform. Also a part of the perturbation arrives during the quiescent part of the pulsatile blood flow waveform and thereby may affect the determination of the zero reference.